Metastatic disease may arise from normal cells that migrate and remain dormant until oncogenes get activated, according to paper in Science.

Cancer metastasis may happen earlier in the disease process than was previously thought, reports investigators at Memorial Sloan-Kettering Cancer Center. They suggest that metastatic disease could arises from normal cells that spread relatively early and remain dormant until cancer genes are switched on.

The researchers injected mice with normal mammary cells that had been experimentally manipulated to allow them to turn on certain cancer genes at various times after the injection.

The scientists found that the normal mammary cells were capable of traveling in the bloodstream to the lungs and surviving there for up to four months without expressing any oncogenes. The cells did not begin growing aggressively in the lungs until the oncogenes had been turned on.

The paper appears in the August 28 edition of the online version of Science.